Commit based on the commit from wrs-switch-sw repo described below. It does
not have impact on PPSI, just for consistency.

userspace/libwr: check shmem consistency in wrs_shm_get_and_check

Check the consistency of shmem during opening with wrs_shm_get_and_check.
It was possible that sequence number was increased during the opening, but it
was interpreted as version error.

Add defines describing different return errors.

This change is backward compatible.
Signed-off-by: Adam Wujek <adam.wujek@cern.ch>